My Mac 1900 has problem with left ch. The line stage will be on with a delay of about 7 to 15 sec. I can trace the culprit as all the transistors are at their respective working volatges. All the capacitors has been changed too with new Rifa and Elna Silmic.
The same channel has an NPN driver transistor burnt out which I have changed to the Tip 35 type ( cant rem but the TIP pair), with the BC shunt capacitor increased by 100pf or so. But then it butrnt again the second time. After that I decided to increase all the input and output shunt caps and it is ok so far.
I hope to sort out the pre amp problem. Perhaps need to change the transistor to the BC 550/560 types.
Next after the line stage is fix I will attempt to change the output power transsitor to complimantary NPN/PNP type.